Colour television display apparatus provided with a picture display tube with electron beams generated in one plane

ABSTRACT

Colour television display apparatus provided with a display tube with electron beams generated in one plane. In order to enlarge the colour selection angle without the necessity of thickening the neck, a statically energized magnetic quadripolar field is generated at the area of the deflection plane while there is no point of intersection of the beams located within the display tube in the absence of this quadripolar field. This is ensured by four extra windings on the core of the deflection coil system, or by the deflection coils themselves if they are toroidally wound, or by four permanent magnets. The beams may be generated in a diverging manner in the display tube.

United States Patent 1191 Barten [111 3,857,057 1451 Dec.2 4, 1974 COLOUR TELEVISION DISPLAY APPARATUS PROVIDED WITH A PICTURE DISPLAY TUBE WITH ELECTRON BEAMS GENERATED IN ONE PLANE [75] Inventor: Piet Gerard Joseph Barten,

Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

[22] Filed: Dec. 15, 1972 [21] Appl. No.: 315,681

[30] Foreign Application Priority Data Dec. 22, 1971 Netherlands 7117623 52] U.S. cl; 313/412 [51] Int. Cl H01j 2 9/76, H04n 3/16 [58] Field of Search 313/70 C, 84

[56] References Cited UNITED STATES PATENTS 2,866,125 12/1958 Haantjes et a1. 313/84 3,035,198 5/1962 Skoyles 313/84 3,191,104 6/1965 Mak..; t 313/84 3,659,133 4/1972 Tsuneta et al. 313/70 3,721,931 3/1973 Wharton 313/84 I Primary ExaminerRona1d L. Wibert Assistant Examiner-Richard A. Rosenberger Attorney, Agent, or FirmFrank' R. Trifari; Henry 1. Steckler [57 ABSTRACT I Colour television display apparatus provided with a display tube with electron beams generated in one plane. In order to enlarge the colour selection angle without the necessity of thickening the neck, a statically energized magnetic quadripolar field is generated at the area of the deflection plane while there is no point of intersection of the beams located within the' display tube in the absence of this quadripolar field.

This is ensured by four extra windings on the core of the deflection coil system, or by the deflection coils themselves if they are toroidally wound, or by four permanent magnets. The beams may be generated in a diverging manner in the display tube.

14 Claims, 8 Drawing Figures Patented Dec. 24, 1974 3,857,057

4 Sheets-Sheet 2 Patented Dec. 24, 1974 3,857,057

4 Sheets-Shae t 1% Patented Dec. 24, 1974 3,857,057

4 Sheets-Sheet 4 COLOUR TELEVISION DISPLAY APPARATUS PROVIDED WITH A PICTUREDISPLAY TUBE WITH ELECTRON BEAMS GENERATED IN ONE PLANE The invention relates to colour television display apparatus provided with a picture display tube having a display screen, and with a system of deflection coils comprising a magnetic core for deflecting electron beams into two substantially orthogonal directions, which beams are generated substantially in one plane in the tube,and with a corrector for adjusting the direction of the electron beams, said corrector being provided on the neck of the display tube between the generating device of the electron beams and the deflection coil system. I

A television display tube of this kind is described, for example, in Netherlands Patent Application No. 7012445. In this tube three electron beams are generated which are located in a substantially horizontal common plane. The neck thereof includes inter alia deflection plates which are present before the position (in the propagation direction of the electrons) where the deflection coil system must be provided externally and before this converging deflection means which are either of the electrostatic or of the magnetic type. The beams can be registered on the display screen by means of these plates andthe said means. This is effected both horizontally and vertically so that the said deflection plates and the said means constitute a corrector whereby the direction of the beams is adjusted in order that they converge towards one point on the screen.

However, in a tube of this kind the mutual distance between two beams is much smaller in case of the same cross-section of the neck than in a tube in'which the guns are placed on the corners of an equilateral triangle. As a result the so-called colourselection angle is much smaller and therefore the colour purity may be affected by interference fields and/or geometrical deviations. Thec'olour selection angle is understood to mean the smallest angle which is located between two beams in a point on the display screen in the converged condition. An object of the present invention is to increase the mutual distance between the beams at the area of the deflection coil system and therefore also to increase I the colour selection angle relative to the known display tubes without changing to a larger crosssection of the neck. To this end the arrangement according to the invention is characterized in that the landing spots of the electron beams on the display screen are also registered by a statically energized magnetic quadripolar field generated at the area of the deflection plane, while there is no point of intersection of the beams located within the display tube in the absence of said quadripolar field.

The deflection plane may be defined in this case as the plane which is at right angles to that in which the electron beams are generated, approximately in the centre of the deflection field generated by the deflection coil system and in which the beams may be considered to be deflected.

Due to the step according to the invention convergence is effected simultaneously with the deflection. It is to be noted that it is known per se from the US. Patent Ser. No. 367,944, filed June 7, 1973 to use a magnetic quadripolar field generated at the area of the deflection plane in order to correct deflection errors,

which field is generated by means of windings wound on the core. The current flowing through these windings is, however, proportional to the square of at least one deflection current so that the field is not static. A static quadripolar field is known from US. Pat. No. 2,907,908, but this field is not generated at the area of the deflection plane;

The invention will be described in detail with reference to the accompanying figures by way of example, and:

FIG. 1 shows a circuit diagram of television display apparatus provided with a display tube in which the electron beams are generated substantially in one plane,

FIG. 2 is a plan view of the paths of the electrons in the display tube of FIG. 1.,

FIGS. 3 and 4 show the system of deflection coils which may be used in the arrangement according to FIG. 1,

FIG. 5 is a principle circuit diagram of an embodiment of the system of deflection coils, and

FIG. 6 shows an enlarged part of FIG. 2.

In FIG. 1, 1 denotes an aerial by which the colour television signal can be received. This colour television signalis applied to an RF and IF amplifier 2 which amplifies and detects the signal and subsequently applies it to a video amplifier 3. This video amplifier 3 applies to a first output 4 the actualvideo signal consisting of a luminance signal and colour difference signals. These signals are processed in a matrix circuit 5 so that the three colour signals R, G, andB become available at the output of this matrix circuit and are applied to the three cathodes K K and K of the cathode-ray tube 6 operating as a colour television display tube. The coloured image is displayed on the screen S of tube 6. The synchronizing signal is derived from a second output 7 of video amplifier 3 and this signal is applied to the line deflection generator 8 on the one hand and to the field deflection generator 9 on the other hand. Two outputs 10 and 11 of generator 8 are connected to the deflection coil system 12 at one end and an output 13 is connected to the final anode of display tube 6 at the other end for delivery of the final anode voltage of approximately 25 kilovolts. The outputs l4 and 15 of field deflection generator 9 are likewise connected to deflection coil system 12 for supplying the field deflection current. As a rule, the line deflection current derived from outputs l0 and 11, together with a deflection unit of deflection coil system 12, ensures the horizontal deflection of the electron beams generated by the'three cathodes K K and K Simultaneously the field deflection current derived from outputs l4 and 15, in cooperation with a further deflection unit of deflection coil system 12, ensures the vertical deflection of the three electron beams. The neck of tube 6 is provided with a corrector 16 to which a direct voltage source 17 applies direct current. A further direct voltage source 18 applies a direct current in a manner to be described hereinafter to deflection coil system 12.

FIG. 2a is a simplifiedplan view of the paths of the electrons is display tube 6. The electron beams B B and B for the colours red, green and blue, respectively, are generated by the three cathodesK K and K and they are modulated in known manner by the colour signals R, G and B. Tube 6 also includes other electrodes which will be. left out of consideration for the sake of simplicity. Cathodes K K and K are arranged in one horizontal plane, in which beam B substantially coincides with the axis of tube 6 while beams B R and B are generated in a diverging manner relative thereto. Corrector 16 consists of, for example, four electromagnets 16 16 and 16 16 (not shown) which are substantially located in the same plane as the beams and whose influence is approximately felt-in a plane C which is at right angles to the plane of FIG. 2a, in which electromagnets 16 RV and 16 ensure the vertical convergence of the red and blue beams, respectively, while electromagnets 16 'and 16 ensure the horizontal convergence thereof. Corrector 16 envisages a pro-correction of the direction of the beams which can berealized by adjusting the direct currents flowing through the said electromagnets. Beams B and B are deflected in the 'plane C but remain in the horizontal plane. In addition they continue to diverge while beam B is substantially not influenced.

Without further steps beams B and B would continue to diverge in the absence of the deflection currents after passing deflection plane D as is shown in broken lines in FIG. 2a. Beam B impinges upon display screen S in the centre M thereof. In the presence of the deflection currents flowing through coil system 12 the beams are horizontally and vertically deflected. Beam B impinges upon screen S at a point P. It is clear that in both cases beams B andB will not impinge upon screen S at the same point as beam B FIG. 3 shows an elevational view at right angles to the axis of tube 6 of the magnetic core 19 f deflection coil system 12 in a direction opposite to the propagation direction of the electron beams B 'B and B in which the deflection coils themselves have not been shown for the sake of simplicity. Four windings 20, 21, 22 and 23 are toroidally wound on core 19 which are arranged, for example, in series and through which a direct current i provided by direct current source 18 flows. Windings 21 and 23 are provided at the area where the X-axis and core 19 cross each other, which X-axis coincides with the horizontal deflection direction, while windings 20 and 22 are provided at the area where the Y-axis and core 19 cross each other, which Yaxis coin cides with the vertical deflection direction. windings 20, 21, 22 and 23 have substantially the same number of turns and consequently generate four substantially identical magnetic fields some lines of force ofwhich are shown by arrows in FIG. 3. The winding sense of the windings is chosen to be such that the said fields in core 19 counteract each other. Under these circumstances the resultant field can be considered as a quadripolar field whose poles are located approximately in the direction of the diagonals U and V of the X-Y- system of axes. It will be evident that other embodiments are possible for which windings 20, 21, 22 and 23 are not identical and/or through which not the same current flows, provided that the fields generated by these windings result in a quadripolar field as described;

FIG. 3 clearly-shows that the quadripolar field in the absence of the deflection field does not exert influence on beam B which, in fact, is located in the centre of plane D. Beams B and B undergo a force directed along the X-axis, which force attempts to bring these beams nearer to each other. Deflection coil system '12 therefore has a converging action. In the presence of the deflection field an influence of beam B is felt, but this converging action remains.

For a given design of the display" tube and of the deflection coil system a fixed direct current through windings 20, 21, 22 and 23 maybe chosen for a satisfactorily converged image. The convergence is to be further adjusted by means of corrector 16. For this purpose the currents flowing through electromagnets 16 16 16 and 16 of corrector- 16 may be separately adjustable. Asa result deviations in the landings of the beams as a result of tolerances of the guns 'may be largely obviated. Under these circumstances it can be ensured that the three beams impinge at points M and P of display screen S.

' FIG. 2b shows the same as FIG. 2a, however, with the difference that beams B and B do not diverge after passing plane C, but converge on the understanding, however, that in the absence of the described quadripolar field they would intersect each other beyond the display screen. The advantage of the step according to the invention is then maintained. The same applies when the cathodes are not arranged in a diverging manner but are arranged parallel toeach other and to the axis of tube 6. in the latter case, likewise as in the case of FIGS. 2a and 2b, angle a, the colour selection angle, is still larger than in the case where the beams would leave plane C in a converging manner towards a point located within tube 6. In FIG. '2 chain-link lines denote the beamsin the known case where the convergence is exclusively effected in planeC.

FIG. 2c shows the situation in which the cathodes run parallel and in which beams B and B leave plane C in a diverging manner. In thismanner they reach plane D still at a greater distance from the axis than in the known arrangements, in other words, colour selection angle a is enlarged. Since the thickness of the neck of the tube is determined by the largest distance in plane C from the extreme beams, in this case B and B the situation according to FIG. 20 has the advantage that the neck can be made still narrower. As a' result both the deflection field and the quadripolar field according to the invention can exert more influence on the beams. I i

It may be noted that the construction of the guns may be of such a good quality that in the embodiments according to FIGS. 2a and 2b no or substantially no current need be applied to corrector 16. In such a case the quadripolar field according to the invention exclusively or substantially exclusively ensures the convergence of the beams.

It may be concluded from FIG. 3 that the same converging effect may be obtained with the aid of windings 21 and 23 only..This is not true. In fact, the magnetic fields induced in core 19 by windings 21 and 23 would circulate in' the core in the absence of windings 20 and 22 without being able to exert a noticeable influence in the space within the core.

The same converging action in deflection-plane D may alternatively be realized with the aid of the saddle coils 20', 21, 22', and 23 of FIG. 4 which coils are provided substantially symmetrically about diagonals UU'and V. FIG. 4 shows that the lines of force of the quadripolar field generated by these coils have the desired direction in the space within core 19 and close within the core. Alternatively, windings 20, 21, 22 and 23 of FIG. 3 may be replaced by four permanent magnets having pole shoes and being provided on the inner side of core 19 at the area where the X and Y-axis cross the core, the magnetisation of the magnets being tangentially directed. In the same manner windings 21', 22 and 23' of FIG. 4 may be replaced by four permanent magnets having pole shoes and being provided on the inner side of core 19 at the area where diagonals U and V cross the core with the magnetisation of the magnets being radially directed.

In the embodiments already described the deflection coils may be formed arbitrarily, that is to say, it is of no importance for the invention whether they are toroidally wound or are wound as saddle coils. However, in the case where the deflection coils are wound toroidally on core 19 they can generate the required quadripolar field according to one aspect of the invention without the necessity of providing an extra winding on the core. For this purpose each deflection coil must be split up into two coil halves which coil halves are to be arranged on core 19 in the same manner as windings 20, 21, 22 and 23 of FIG. 3. A possible embodiment of this principle is shown in a very diagrammatical way in FIG. 5. In this case windings 20 and 22 are the coil halves for the vertical deflection and are arranged in parallel. In a similar manner windings 21 and 23 are likewise arranged in parallel and are the coil halves for the horizontal deflection. The deflection generators 8 and 9 of FIG. 1 provide the line deflection current i and the field deflection current i respectively. Direct voltage sources 18' and 18" are arranged in series with a coil half, for example, coil halves 21 and 22, respectively. The direct currents i and i" provided by sources 18 and 18", respectively, are added to deflection currents i and i in one coil half, for example, 21 and 20, respectively, while currents i and i in the other coil halves 23 and 22 are subtracted from deflection currents i), and i respectively. When sources 18 and 18" are proportioned in such a manner that the fields generated by currents i and i" are substantially equal, coil I halves 20, 21, 22 and 23 generate the desired quadripolar field. It will be noted that deflection generators 8 and 9 also provide direct currents for centring the displayed image on screen S. These direct currents are, however, identical for the relevant deflection coil halves 20, 22 and 21, 23 and consequently do not generate a quadripolar field.

In the case where a dynamic correction of the convergence is' necessary, it can be performed with the aid of a quadripolar field generated by windings 20, 21, 22 and 23 of FIG. 3 and 5 or windings 20, 21', 22' and 23' of FIG. 4. A line and/or field frequency sawtooth current which is adjustable. if necessary, may be superimposed, for example, on the current provided by the source 18, and sources 18' and 18".

Due to the step according to the invention the colour selection angle is enlarged without the necessity of thickening the cross-section of the neck of the display tube. It may even become narrower. This is an advantage which will now be described in detail.

FIG. 6 shows an enlarged part of FIG. 2 in the vicinity of display screen S in which a shadow mask is denoted by m Line B denotes the red electron beam for known arrangements, line 8 shows the same beam for the'arrangement according to the invention. Beam B passes through a hole in mask m, and impinges upon screen S at a point M in its centre in which a green luminescing phosphor dot is provided, while beam B passes through a hole in mask m, and impinges upon screen S at a point M R in which a red luminescing phosphor dot is provided. Since beam B landsunder a larger angle than beam B it impinges upon screen S at the same point M if the shadow mask in m is placed nearer to screen S. As a result the landing, that is to say, the colour purity is less sensitive to magnetic interference fields as will now be described. Such fields are generated, for example, by transformers which are.

present in the television display apparatus or by the earth magnetism field. It is true that the display tube is somewhat screened from such fields but nevertheless they exert a given influence within the tube. As a result the beams of FIG. 6 do not land under the angles shown but under angles which deviate to a slight extent. The landing error then occurring is approximately proportional to the deviation of the angle of the relevant beam caused by the interference fields and to the distance between the shadow mask and the screen. The same applies to the'landing errors which may be caused by deviations in the geometry of the different components of the display tube and/or in the position of the deflection plane D with the landing being effected under an angle which deviates to a slight extent. For these reasons it is advantageous to place the mask nearer to the screen.

Although in the foregoing a display tube in which the electron beams are substantially generated in one horizontal plane has been referred to, it will be evident that the invention may alternatively be used if the generating device of the beams is located in' a differently directed plane, for example, avertical plane. A display tube employing three cathodes has also been referred to. The invention is, however, also usable for, for example, multi-beam cathode ray tubes employing one cathode and also for tubes other than those of the shadow mask type.

What is claimed is:

1. Colour television display apparatus provided with a picture display tube having a display screen, and with a system of deflection coils comprising a magnetic core for deflecting electron beams into two substantially orthogonal directions, which beams are generated substantially in one plane in the tube, characterized in that the landing spots of the electron beams on the display screen are registered by a statically energized magnetic quadripolar field generated at the area of the deflection plane, while there is no point of intersection of the beams located withinthe display tube in the absence of said quadripolar field. A

2. Television display apparatus as claimed in claim 1, characterized in that the quadripolar field is generated by four extra windings toroidally wound on the core at the area where the deflection directions cross the core and through which a direct current flows.

3. Television display apparatus as claimed in claim 1, characterized in that'the quadripolar field is generated by the deflection coils which are toroidally wound on the core, each coil being split up into two halves and a direct current flowing through each coil.

4. Television display apparatus as cliamed in claim 1, characterized in that the quadripolar field is generated by four permanent magnets having pole shoes and being provided on the inner side of the core at the area where the deflection directions cross the core and whose magnetisation is tangentially directed.

5. Television display apparatus as claimed in claim 1, characterized in that the quadripolar field is generated by four extra windings which are wound on the core as saddle coils in directions which are shifted approximately 45 relative to the deflection directions.

6. Television display apparatus as claimed in claim 1, characterized in that the quadripolar field is generated by four permanent magnets having pole shoes and being provided on the inner side of the core at the area where the directions which are shifted approximately 45 relative to the deflection direction cross the core and whose magnetisation is radially directed.

7. Television display apparatus as claimed in claim 1, characterized in that the electron beams are generated in a diverging manner.

8. Television display apparatus as claimed in claim 1, further comprising corrector means for adjusting the direction of the electron beams disposed on the neck of said display tube between the electron beam generating device and said deflection coil system and characterized in that the mutual distance between the electron beams is larger in the deflection plane than at the area of the corrector.

9. An apparatus as claimed in claim 1 comprising a magnetic core on which deflection coils are wound, characterized in that four extra windings are toroidally wound on the core at the area where the deflection directions cross the core.

10. An apparatus as claimed in claim 1 comprising a magnetic core on which deflection coils are wound, characterized in that four permanent magnets having pole shoes are provided on the inner side of the core at the area where the deflection directions cross the core and whose magnetisation is tangentially directed.

11. An apparatus as claimed in claim 1 comprising a I magnetic core on which deflection coils are wound,

characterized in that four extra windings are wound as saddle coils on the core in directions which are shifted approximately 45 relative to the deflection direction.

12. An apparatus as claimed in claim 1 comprising a magnetic core on which deflection coils are wound, characterized in that four permanent magnets having pole shoes are provided on the inner side of the core at the area where directions which are shifted approximately 45 relative to the deflection directions cross the core and whose magnetisation is radially directed.

13. A device as claimed in claim 1 further comprising means disposed on the neck of said tube between the electron beam generating device and said magnetic core for adjusting the direction of said electron beams.

said beams to interfering fields. 

1. Colour television display apparatus provided with a picture display tube having a display screen, and with a system of deflection coils comprising a magnetic core for deflecting electron beams into two substantially orthogonal directions, which beams are generated substantially in one plane in the tube, characterized in that the landing spots of the electron beams on the display screen are registered by a statically energized magnetic quadripolar field generated at the area of the deflection plane, while there is no point of intersection of the beams located within the display tube in the absence of said quadripolar field.
 2. Television display apparatus as claimed in claim 1, characterized in that the quadripolar field is generated by four extra windings toroidally wound on the core at the area where the deflection directions cross the core and through which a direct current flows.
 3. Television display apparatus as claimed in claim 1, characterized in that the quadripolar field is generated by the deflection coils which are toroidally wound on the core, each coil being split up into two halves and a direct current flowing through each coil.
 4. Television display apparatus as cliamed in claim 1, characterized in that the quadripolar field is generated by four permanent magnets having pole shoes and being provided on the inner side of the core at the area where the deflection directions cross the core and whose magnetisation is tangentially directed.
 5. Television display apparatus as claimed in claim 1, characterized in that the quadripolar field is generated by four extra windings which are wound on the core as saddle coils in directions which are shifted approximately 45* relative to the deflection directions.
 6. Television display apparatus as claimed in claim 1, characterized in that the quadripolar field is generated by four permanent magnets having pole shoes and being provided on the inner side of the core at the area where the directions which are shifted approximately 45* relative to the deflection direction cross the core and whose magnetisation is radially directed.
 7. Television display apparatus as claimed in claim 1, characterized in that the electron beams are generated in a diverging manner.
 8. Television display apparatus as claimed in claim 1, further comprising corrector means for adjusting the direction of the electron beams disposed on the neck of said display tube between the electron beam generating device and said deflection coil system and characterized in that the mutual distance between the electron beams is larger in the deflection plane than at the area of the corrector.
 9. An apparatus as claimed in claim 1 comprising a magnetic core on which deflection coils are wound, characterized in that four extra windings are toroidally wound on the core at the area where the deflection directions cross the core.
 10. An apparatus as claimed in claim 1 comprising a magnetic core on which deflection coils are wound, characterized in that four permanent magnets having pole shoes are provided on the inner side of the core at the area where the deflection directions cross the core and whose magnetisation is tangentially directed.
 11. An apparatus as claimed in claim 1 comprising a magnetic core on which deflection coils are wound, characterized in that four extra windings are wound as saddle coils on the core in directions which are shifted approximately 45* relative to the deflection direction.
 12. An apparatus as claimed in claim 1 comprising a magnetic core on which deflection coils are wound, characterized in that four permanent magnets having pole shoes are provided on the inner side of the core at the area where directions which are shifted approximately 45* relative to the deflection directions cross the core and whose magnetisation is radially directed.
 13. A device as claimed in claim 1 further comprising means disposed on the neck of said tube between the electron beam generating device and said magnetic core for adjusting the direction of said electron beams.
 14. A device for a display tube having a gun for generating a plurality of coplanar electron beams having no intersection point within said tube, said device comprising means disposed on said tube for deflecting said beams substantially at an effective deflection plane, and convergence means disposed on said tube for generating at least a static quadripolar magnetic field substantially at said deflection plane for converging said beams within said tube, whereby a large color selection angle results, thereby minimizing the susceptibility of said beams to interfering fields. 